U.S. patent application number 14/505290 was filed with the patent office on 2015-02-26 for method of forming metal oxide hardmask.
The applicant listed for this patent is ASM Japan K.K.. Invention is credited to Hideaki Fukuda.
Application Number | 20150056540 14/505290 |
Document ID | / |
Family ID | 46317718 |
Filed Date | 2015-02-26 |
United States Patent
Application |
20150056540 |
Kind Code |
A1 |
Fukuda; Hideaki |
February 26, 2015 |
Method of Forming Metal Oxide Hardmask
Abstract
A method of forming a metal oxide hardmask on a template
includes: providing a template constituted by a photoresist or
amorphous carbon formed on a substrate; and depositing by atomic
layer deposition (ALD) a metal oxide hardmask on the template
constituted by a material having a formula
Si.sub.xM.sub.(1-x)O.sub.y wherein M represents at least one metal
element, x is less than one including zero, and y is approximately
two or a stoichiometrically-determined number.
Inventors: |
Fukuda; Hideaki; (Tokyo,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ASM Japan K.K. |
Tokyo |
|
JP |
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|
Family ID: |
46317718 |
Appl. No.: |
14/505290 |
Filed: |
October 2, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13333420 |
Dec 21, 2011 |
8901016 |
|
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14505290 |
|
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61427661 |
Dec 28, 2010 |
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Current U.S.
Class: |
430/5 ;
438/786 |
Current CPC
Class: |
H01L 21/0337 20130101;
H01L 21/0228 20130101; H01L 21/02186 20130101; H01L 21/02274
20130101; H01L 21/02153 20130101; G03F 1/00 20130101; H01L 21/0215
20130101 |
Class at
Publication: |
430/5 ;
438/786 |
International
Class: |
H01L 21/02 20060101
H01L021/02; G03F 1/00 20060101 G03F001/00; H01L 21/033 20060101
H01L021/033 |
Claims
1. A method of forming a metal oxide hardmask on a template,
comprising: providing a template constituted by a photoresist or
amorphous carbon formed on a substrate; and depositing by atomic
layer deposition (ALD) a metal oxide hardmask on the template
constituted by a material having a formula
Si.sub.xM.sub.(1-x)O.sub.y wherein M represents at least one metal
element, x is less than one including zero, and y is approximately
two or a stoichiometrically-determined number, wherein the metal
oxide hardmask is constituted by a laminate of atomic layers of a
metal oxide and atomic layers of a silicon oxide alternately
deposited at a cycle ratio C such that the laminate has the formula
Si.sub.xM.sub.(1-x)O.sub.y, where C=m/(m+n) where m is the number
of cycles for metal oxide consecutive layers, and n is the number
of cycles for silicon oxide consecutive layers.
2. The method according to claim 1, wherein the cycle ratio is
adjusted in a range of over 0/1 and less than 1/1.
3. The method according to claim 1, wherein the metal oxide
hardmask is a spacer film.
4. The method according to claim 3, wherein the spacer film is for
spacer-defined double patterning (SDDP), and the method further
comprises performing SDDP after the step of depositing the spacer
film on the template.
5. The method according to claim 1, wherein M is a metal whose
fluoride has a vapor pressure of more than 100 Pa at a temperature
for cleaning a reactor used for depositing the metal oxide
hardmask.
6. The method according to claim 5, wherein M is Ti, W, or Ta.
7. The method according to claim 6, wherein M is Ti.
8. The method according to claim 7, wherein the material
constituting the metal oxide hardmask is TiO.sub.2.
9. The method according to claim 1, wherein the ALD is plasma
enhanced ALD (PE-ALD).
10. The method according to claim 1, wherein the ALD is performed
at a temperature of 300.degree. C. or lower for the template
constituted by the amorphous carbon or at a temperature of
150.degree. C. or lower for the template constituted by the
photoresist.
11. The method according to claim 1, wherein the ALD is performed
under conditions substantially equivalent to those set for a
SiO.sub.2 hardmask constituted by SiO.sub.2, wherein a gas
containing M is used in place of a gas containing Si for the
SiO.sub.2 hardmask.
12. The method according to claim 11, wherein the metal oxide
hardmask has an elastic modulus at least three times higher than
that of the SiO.sub.2 hardmask, and a hardness at least two times
higher than that of the SiO.sub.2 hardmask.
13. The method according to claim 11, wherein the metal oxide
hardmask has a dry etch rate lower than that of the SiO.sub.2
hardmask and a wet etch rate comparable to that of standard thermal
oxide.
14. The method according to claim 1, wherein the substrate has a
base film formed under the template, which base film is constituted
by silicon oxide.
15. The method according to claim 1, wherein the template has a
convex pattern constituted by the photoresist or amorphous carbon,
said convex pattern having a width of less than one micron meter
and a ratio of height to width of one or higher.
16. The method according to claim 9, wherein the depositing of the
metal oxide hardmask comprises supplying a precursor for the metal
oxide hardmask in pulses and applying RF power in pulses between
the pulses of the precursor, wherein at least one reactant gas is
supplied while applying the RF power, wherein the precursor is a
metal-containing alkylamino compound or metal-containing alkoxy
compound.
17. The method according to claim 16, wherein the reactant gas
comprises a nitrogen-containing gas.
18. A metal oxide hardmask deposited on a template, constituted by
a material having a formula Si.sub.xM.sub.(1-x)O.sub.y wherein M
represents at least one metal element selected from Ti, W, or Ta, x
is more than zero but less than one, and y is approximately two or
a stoichiometrically-determined number, wherein the metal oxide
hardmask is constituted by a laminate of atomic layers of a metal
oxide and atomic layers of a silicon oxide alternately deposited at
a cycle ratio C such that the laminate has the formula
Si.sub.xM.sub.(1-x)O.sub.y, where C=m/(m+n) where m is the number
of cycles for metal oxide consecutive layers, and n is the number
of cycles for silicon oxide consecutive layers.
19. The metal oxide hardmask according to claim 18, wherein the
metal oxide is TiO.sub.2, and the silicon oxide is SiO.sub.2.
20. The metal oxide hardmask according to claim 18, wherein the
proportion of metal oxide relative to the mixture of metal oxide
and silicon oxide varies in a thickness direction of the laminate
as the cycle ratio varies.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation of U.S. patent application Ser. No.
13/333,420, filed Dec. 21, 2011, which claims the benefit of U.S.
Provisional Application No. 61/427,661, filed Dec. 28, 2010, each
disclosure of which is herein incorporated by reference in its
entirety for some applicable embodiments disclosed herein.
[0002] The applicant herein explicitly rescinds and retracts any
and all prior disclaimers or disavowals made in any parent, child
or related prosecution history with regard to any subject matter
supported by the present application.
BACKGROUND
[0003] The present invention relates to semiconductor integrated
circuit manufacturing and, more particularly to a method of forming
a hardmask, particularly a spacer film.
DESCRIPTION OF THE RELATED ART
[0004] Photolithography technology has recently faced difficulty of
forming patterns having pitches smaller than the submicron level.
Various approaches have been studied, and one of the promising
methods is space-defined double patterning (SDDP) which makes it
possible to create narrow pitches beyond limitations of
conventional lithography such as light source wavelength and high
index immersion fluid. Generally, SDDP needs one conformal spacer
film and hardmask template wherein the conformal spacer film is
deposited on the template normally having convex patterns. A
silicon oxide layer is commonly used as a conformal spacer, and a
hardmask template is typically constituted by photoresist (PR) or
amorphous carbon (a-C) prepared by a spin-on or CVD process.
[0005] As discussed blow, the present inventors have recognized
several problems in SDDP and developed solutions thereto, which
solutions can also be applicable to general patterning processes.
Thus, the present invention relates to improvement on general
patterning processes using a hardmask, and particularly on
SDDP.
[0006] Any discussion of problems and solutions involved in the
related art has been included in this disclosure solely for the
purposes of providing a context for the present invention, and it
should not be taken as an admission that any or all of the
discussion was known at the time the invention was made.
[0007] In SDDP process flow, it is required for a spacer film to be
etch-selective relative to a base film which is typically a bottom
antireflective coating (BARC) or a hardmask having BARC functions.
The base film is typically constituted by a material such as SiO,
SiOC, TiN-HM, etc. which is typically formed by CVD. Typically, as
a spacer film, a low-temperature SiO film (LT-SiO) which is formed
by atomic layer deposition (ALD) at low temperatures is used.
However, the LT-SiO does not have sufficient etch (dry and/or wet)
selectivity relative to a base film, thereby causing unexpected
critical dimension (CD) changes or the like.
[0008] Most metal oxides/nitrides are known to be etch-selective to
SiO. Some metal oxides are hardly etched by dry etch. That is a
significant concern for semiconductor integration and also reactor
cleaning. For example, Al.sub.2O.sub.3 is one of the promising
candidate materials, because it has a 100% conformal film profile
even at room temperature and has high etch selectivity relative to
a base film. However, Al.sub.2O.sub.3 is known to be hardly etched
by dry etch and/or wet etch, prohibiting Al.sub.2O.sub.3 from being
used as a spacer material.
[0009] Further, it is required that a spacer film be formed at low
deposition temperatures such as less than 150.degree. C. when the
template is constituted by photoresist, or less than 300.degree. C.
when the template is constituted by amorphous carbon. Otherwise,
the template may be damaged by heat during the deposition of the
spacer film, and additionally, if the temperature is as high as
400.degree. C., diffusion or migration of Cu or B into a device
such as an insulation film, wiring, or transistor may occur.
Namely, the spacer film needs to be compatible with the template.
Also, it is required for the spacer film to be substantially 100%
conformal and have substantially no pattern loading effect (e.g.,
substantially the same thickness on sidewalls even when the density
of patterns or pitch of patterns is different). Conventional spacer
films do not satisfy the above criteria. Additionally, a metal such
as V or Nb which is not commonly used in the semiconductor
processing processes may not be a good candidate.
[0010] Many groups have studied conformal SiN deposition, but their
attempts have not yet been successful to provide a solution to
obtaining conformal SiN film. At a low temperature such as
400.degree. C. or lower, a SiN process fails to form a conformal
film ("conformal" refers to a Ts/Tt> about 95% wherein Ts and Tt
are thicknesses on a sidewall and top surface, respectively), and
the low-temperature SiN process is performed at an extremely
low-growth rate such as less than 0.1 nm/min.
[0011] The present inventors have recognized still another problem
in SDDP which is a problem of patterned spacer collapsing. FIGS. 1A
to 1D are a schematic representation illustrating a part of the
SDDP sequence of (a) photoresist (PR) patterning (FIG. 1A), (b) SiO
deposition by PE-ALD (FIG. 1B), (c) reactive ion etch (RIE) (FIG.
1C), and (d) PR ashing (FIG. 1D). This figure is solely for
addressing the above problem and does not necessarily represent
conventional technology. As shown in FIGS. 1A to 1D, in step (a),
PR 2 (template) is formed in a pattern on a base film 1 (BARC or
hardmask), under which a target film 4 to be etched is formed. In
step (b), a spacer film 3 is deposited on and covers PR 2 and the
base film 1. In step (c), anisotropic spacer etching is conducted,
and as a result, the top of PR 2 and the base film 1 are exposed,
thereby forming an exposed PR 2' and a spacer 3'. In step (d), the
exposed PR 2' is removed by etching, and as a result, the spacer 3'
collapses, deteriorating the pattern.
[0012] The main cause of collapse appears to be capillary force
during the process of drying residual rinse and water after the
template (PR 2') is removed by ashing. The pattern collapse problem
becomes more serious when patterns are as narrow as the submicron
level and have higher aspect ratios such as one or higher. FIG. 2
is a schematic representation illustrating capillary force
generated during the drying process. Capillary force
.sigma..sub.max (maximum stress exerted on the spacer) is expressed
by the following equation (Y. Matsui et al., ISSM 2010, Tokyo,
PO-O-103):
.sigma. max = 6 .gamma. cos .theta. D ( H W ) 2 ##EQU00001##
[0013] .gamma.: surface tension of H.sub.2O
[0014] .theta.: H.sub.2O contact angle
[0015] D: space width
[0016] H: height
[0017] W: width
[0018] In the figure, a spacer 21 is formed on a base film 23, and
a space 22 between the spacers 21 is filled with water. The top of
filled water is concave as it is being dried. The maximum stress
exerted on the spacer 21 strongly depends on the aspect ratio (H/W)
and the contact angle (A).
[0019] One approach to solve this problem is using a hydrophobic
material so as to reduce capillary force. However, it is very
difficult to maintain hydrophobicity of the surface of the spacer
for SDDP because even if the hydrophobic material is used, after
ashing (typically by exposing the template to an oxidant plasma
such as an oxygen plasma, N.sub.2O plasma, and CO.sub.2 plasma, the
surface is easily changed to hydrophilic because hydrophilic O--H
is easily generated on the oxidized surface after air exposure.
SUMMARY
[0020] As discussed above, the present inventors have recognized
several problems in SDDP and developed solutions thereto. The
solutions can also be applicable to general patterning processes.
Some embodiments of the present invention provide solutions to at
least one of the above problems, and some embodiments provide
solutions to all of the above problems.
[0021] An embodiment of the present invention provides a method of
forming a metal oxide hardmask on a template, comprising: (i)
providing a template constituted by a photoresist or amorphous
carbon formed on a substrate; and (ii) depositing by atomic layer
deposition (ALD) a metal oxide hardmask on the template constituted
by a material having a formula Si.sub.xM.sub.(1-x)O.sub.y wherein M
represents at least one metal element, x is less than one including
zero, and y is approximately two or a stoichiometrically-determined
number. The "hardmask" refers to a material used in any
semiconductor processing as an etch mask in lieu of polymer or
other organic "soft" materials (target films) which tend to be
etched easily by oxygen, fluorine, chlorine, or other reactive
gases to the extent that a pattern defined using the "soft" mask
can be rapidly degraded during plasma etching as compared with the
hardmask.
[0022] In some embodiment, the metal oxide hardmask is a spacer
film. In some embodiments, the spacer film is for spacer-defined
double patterning (SDDP), and the method further comprises
performing SDDP after the step of depositing the spacer film on the
template.
[0023] In some embodiments, M is a metal whose fluoride has a vapor
pressure of more than 100 Pa at a temperature for cleaning a
reactor used for depositing the metal oxide hardmask. In some
embodiments, M is Ti, W, or Ta. In some embodiments, M is Ti. In
some embodiments, the material constituting the metal oxide
hardmask is TiO.sub.2.
[0024] In some embodiments, the ALD is plasma enhanced ALD
(PE-ALD). In some embodiments, the ALD is performed at a
temperature of 300.degree. C. or lower for the template constituted
by the amorphous carbon or at a temperature of 150.degree. C. or
lower for the template constituted by the photoresist. In some
embodiments, the ALD is performed under conditions substantially
equivalent to those set for a SiO.sub.2 hardmask constituted by
SiO.sub.2, wherein a gas containing M is used in place of a gas
containing Si for the SiO.sub.2 hardmask. In some embodiments, the
metal oxide hardmask has an elastic modulus at least three times
higher than that of the SiO.sub.2 hardmask, and a hardness at least
two times higher than that of the SiO.sub.2 hardmask. In some
embodiments, the metal oxide hardmask has a dry etch rate lower
than that of the SiO.sub.2 hardmask and a wet etch rate comparable
to that of standard thermal oxide.
[0025] In some embodiments, the substrate has a base film formed
under the template, which base film is constituted by silicon
oxide. In some embodiments, the template has a convex pattern
constituted by the photoresist or amorphous carbon, said convex
pattern having a width of less than one micron meter and a ratio of
height to width of one or higher.
[0026] For purposes of summarizing aspects of the invention and the
advantages achieved over the related art, certain objects and
advantages of the invention are described in this disclosure. Of
course, it is to be understood that not necessarily all such
objects or advantages may be achieved in accordance with any
particular embodiment of the invention. Thus, for example, those
skilled in the art will recognize that the invention may be
embodied or carried out in a manner that achieves or optimizes one
advantage or group of advantages as taught herein without
necessarily achieving other objects or advantages as may be taught
or suggested herein.
[0027] Further aspects, features and advantages of this invention
will become apparent from the detailed description which
follows.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] These and other features of this invention will now be
described with reference to the drawings of preferred embodiments
which are intended to illustrate and not to limit the invention.
The drawings are oversimplified for illustrative purpose and are
not necessarily to scale.
[0029] FIGS. 1A to 1D is a schematic representation illustrating a
part of the SDDP sequence of (a) photoresist (FIG. 1A), (PR)
patterning (FIG. 1A), (b) SiO deposition by PE-ALD (FIG. 1B), (c)
reactive ion etch (RIE) (FIG. 1C), and (d) PR ashing (FIG. 1D).
[0030] FIG. 2 is a schematic representation illustrating capillary
force generated during the drying process.
[0031] FIGS. 3A and 3B is a schematic representation illustrating
in-situ footing reduction where (a) reactive ion etch (RIE) (FIG.
3A) and (b) ashing (FIG. 3B) are conducted.
[0032] FIGS. 4A to 4G schematically illustrate SDDP processes
wherein (a) is a schematic cross sectional view of pre-patterned
features formed on a hardmask (FIG. 4A), (b) is a schematic cross
sectional view of conformal spacer deposition (FIG. 4B), (c) is a
schematic cross sectional view of anisotropic spacer etching (FIG.
4C), (d) is a schematic cross sectional view of removal of the
pre-patterned features (FIG. 4D), (e) is a schematic cross
sectional view of pattern transfer by anisotropic etching (FIG.
4E), (f) is a schematic cross sectional view of transferred pattern
profile (FIG. 4F), and (g) is a schematic cross sectional view of
removal of the spacer (FIG. 4G).
[0033] FIG. 5 illustrates elastic modulus and hardness of each
spacer film deposited in the examples.
[0034] FIG. 6 is a schematic representation of a PE-ALD apparatus
for depositing a spacer film usable in one embodiment of the
present invention.
[0035] FIG. 7 illustrates a process sequence of one cycle of PE-ALD
according to an embodiment of the present invention.
[0036] FIG. 8A is a schematic representation of pattern transfer
and target etching according to a comparative example. FIG. 8B is a
schematic representation of pattern transfer and target etching
according to an embodiment of the present invention.
[0037] FIG. 9 is a schematic representation of pattern transfer and
target etching using space defined double patterning (SDDP)
according to an embodiment of the present invention.
[0038] FIG. 10 is a graph illustrating the relationship between
refractive index (at 633 nm) and average growth rate (nm/cycle) in
relation to the ALD cycle ratio of TiO.sub.2/(TiO.sub.2+SiO.sub.2)
according to embodiments of the present invention.
DETAILED DESCRIPTION
[0039] In this disclosure, "gas" may include vaporized solid and/or
liquid and may be constituted by a mixture of gases. In this
disclosure, the reactant gas, the additive/carrier gas, and the
precursor may be different from each other or mutually exclusive in
terms of gas types, i.e., there is no overlap of gases among these
categories. In some embodiments, "film" refers to a layer
continuously extending in a direction perpendicular to a thickness
direction substantially without pinholes to cover an entire target
or concerned surface, or simply a layer covering a target or
concerned surface. In some embodiments, "layer" refers to a
structure having a certain thickness formed on a surface or a
synonym of film. Further, "a" refers to a species or a genus
including multiple species. In this disclosure, any defined
meanings do not necessarily exclude ordinary and customary meanings
in some embodiments. In the disclosure, "substantially higher",
"substantially different", etc. refer to a difference of at least
10%, 50%, 100%, 200%, 300%, or any ranges thereof, for example.
Also, in the disclosure, "substantially the same", "substantially
equivalent", "substantially uniform", etc. refer to a difference of
less than 20%, less than 10%, less than 5%, less than 1%, or any
ranges thereof, for example. The numerical numbers applied in
examples may be modified by a range of at least .+-.50% in other
conditions, and further, in this disclosure, any ranges indicated
may include or exclude the endpoints. In the present disclosure
where conditions and/or structures are not specified, the skilled
artisan in the art can readily provide such conditions and/or
structures, in view of the present disclosure, as a matter of
routine experimentation.
[0040] In some embodiments, in order to solve at least one or all
of the problems discussed above in patterning processes using a
hardmask, a hardmask material is selected. In some embodiments, a
hardmask material is selected from candidate materials using at
least one or all of the following criteria, for example: a material
has high mechanical strength, and has a low dry and/or wet etch
rate, but it can be etched by fluorine gas, and its fluoride is not
solid at a reactor-cleaning temperature, and further, it can be
deposited by ALD at low temperatures such as 400.degree. C. or
lower.
[0041] In some embodiments, hardmask materials can be selected
using at least one or all of the following criteria:
[0042] 1) A hardmask material has a higher mechanical strength than
that of a conventional SiO hardmask. For example, the hardmask
formed by ALD constituted by the material has an elastic modulus
which is substantially higher than that of a conventional SiO
hardmask formed by ALD at a low temperature, e.g., 150.degree. C.,
and which is at least substantially equivalent to that of a
conventional SiN hardmask formed by ALD at a low temperature, e.g.,
150.degree. C. Also, the hardmask formed by ALD constituted by the
material has a hardness which is substantially higher than that of
a conventional SiO hardmask formed by ALD at a low temperature,
e.g., 150.degree. C., and which is comparable to that of a
conventional SiN hardmask formed by ALD at a low temperature, e.g.,
150.degree. C.
[0043] 2) The hardmask material having a higher chemical resistance
(low dry etch rate) than a conventional SiO hardmask. For example,
the hardmask formed by ALD constituted by the material has a dry
etch rate (NF.sub.3 at 100.degree. C.) which is substantially lower
than that of a conventional SiO hardmask formed by ALD at a low
temperature, e.g., 150.degree. C., and which is also lower than
that of standard thermal oxide. Also, the hardmask formed by ALD
constituted by the material has a wet etch rate (DHF at 1:100)
which is substantially lower than that of a conventional SiO
hardmask formed by ALD at a low temperature, e.g., 150.degree. C.,
and which is substantially comparable to that of standard thermal
oxide.
[0044] 3) The hardmask material contains at least one type of metal
element, and oxygen and/or nitrogen. The material may be expressed
by a formula Si.sub.xM.sub.(1-x)O.sub.y wherein M represents at
least one metal element, x is less than one including zero, and y
is approximately two or a stoichiometrically-determined number. For
example, titanium oxide (e.g., TiO.sub.2) and titanium silicon
oxide (e.g., TiSiO.sub.4), are included.
[0045] 4) The hardmask material is constituted by a metal oxide
(e.g., TiO.sub.2) and a silicon oxide (e.g., SiO.sub.2, non-metal
silicon oxide) so as to effectively adjust a refractive index and a
growth rate. In order to mix a metal oxide and a silicon oxide, the
following methods can be performed in some embodiments: depositing
thin films of the metal oxide and thin films of the silicon oxide
alternately (each film having a thickness of about 3 nm or higher);
depositing a film by introducing a mixture of precursors for the
metal oxide and the silicon oxide; or depositing a film by
alternately introducing a precursor for the metal oxide and a
precursor of the silicon oxide. For example, a hardmask (metal
silicon oxide, e.g., Ti.sub.xSi.sub.(1-x)O.sub.2, 0<x.ltoreq.1)
can be formed by alternately depositing a metal oxide film and a
silicon oxide film by ALD at a certain cycle ratio (a ratio of
cycles for the metal oxide film to cycles for the silicon oxide
film), wherein the growth rate of the silicon oxide is about 2.5
times higher than that of the metal oxide, and the refractive index
of the silicon oxide is lower than that of the metal oxide, so that
by adjusting the cycle ratio, the growth rate and the refractive
index of the resultant hardmask can be adjusted. For example, when
the cycle ratio is one (i.e., one cycle for the metal oxide film
and one cycle for the silicon oxide film are alternately
performed), the composition ratio of metal oxide to silicon oxide
in the hardmask is about 1/2.5 since the growth rate of the silicon
oxide is about 2.5 times higher than that of the metal oxide. By
adjusting the cycle ratio, the proportion of metal oxide relative
to the mixture of metal oxide and silicon oxide can vary from over
0% up to 100%.
[0046] 5) The hardmask material contains at least one metal
element, Si, and oxygen and/or nitrogen to tune optimal mechanical
strength and dry etch rate. In some embodiments, this type of film
can be formed by the methods disclosed in U.S. Pat. No. 7,824,492,
the disclosure of which is herein incorporated by reference.
[0047] 6) The hardmask can be formed by process steps including the
steps described below by using the same reactor as that for forming
a target film, a base film, and a template. This series of steps
can be performed continuously. In the above, "continuously" refers
to without breaking a vacuum, without interruption as a timeline,
without moving the substrate, or immediately thereafter, as a next
step. Although the hardmask can be deposited by ALD whereas the
target film and base film can be deposited by CVD, these reactions
can be accomplished in the same reactor.
[0048] 6-1) Step of evaporating water from a template by baking:
The template is subjected to heat which is subsequently generated
by exposing the template to an inactive gas (e.g., He, Ar, or
N.sub.2) plasma or radicals, so as to evaporate water adsorbed on a
surface of the template in a clean room outside the reactor,
wherein the amount of adsorbed water depends on how long the
template is exposed to air in the clean room.
[0049] 6-2) Step of trimming and/or footing reduction using an
oxygen-containing gas (e.g., N.sub.2O or CO.sub.2).
[0050] 6-3) Step of depositing an adhesion layer on a base film or
treating a surface of the base film by a plasma in order to enhance
adhesion between the hardmask (spacer) and the base film.
[0051] 6-4) Step of depositing a spacer film by ALD (which is
described later).
[0052] 6-5) Step of post treatment: The spacer film can be treated
by post treatment such as thermal annealing, plasma treatment, UV
irradiation, radical exposure by using remote plasma, in order to
prevent moisture adsorption.
[0053] 7) The hardmask is formed by ALD. The deposition methods
include plasma (both remote and in-situ) generation to activate
reactant to cause deposition. A dry/wet etch rate and mechanical
strength can be controlled by using multiple materials for the
hardmask at a certain ratio, forming a composite film. The
preparation of the composite film can be performed by at least one
of the following: a) alternating a step of supplying one precursor
and a step of supplying a different precursor to form one film on
top of another and repeating the steps; b) depositing a film by
supplying a mixed precursor containing multiple precursors; and c)
depositing a film by separately supplying multiple discrete
precursors simultaneously. The deposition temperature may be less
than 300.degree. C. when the template is constituted by amorphous
carbon, or less than 150.degree. C. when the template is
constituted by photoresist.
[0054] 8) The hardmask contains a metal whose fluoride is not solid
at a reactor-cleaning temperature, e.g., less than 400.degree. C.,
so that an unwanted film deposited on an inner wall of the reactor
can easily be removed by a fluorine-containing cleaning gas.
[0055] Some embodiments will be explained below, but the
embodiments are not intended to limit the present invention.
[0056] The metal oxide hardmask is constituted by an oxide of Ti,
W, and/or Ta. In some embodiments, an oxide of Mn, Hf, and/or Ru
can be used in place of or in combination with Ti, W, and/or Ta.
However, preferably, titanium oxide, tungsten oxide, and/or
tantalum oxide in view of material compatibility with semicondutor
processing. The hardmask is deposited by ALD, preferably PE-ALD.
For example, a precursor for titanium oxide can be at least one
compound selected from titanium alkoxide and alkylamino titanium,
including Ti(OR).sub.4 wherein R is independently CxHy (x=0, 1, 2,
3, 4, or 5, y=2x+1), and each R can be different (e.g.,
Ti(OCH.sub.3).sub.2(OC.sub.2H.sub.5)(OC.sub.3H.sub.7));
Ti(NR.sub.2).sub.4 wherein R is independently CxHy (x=0, 1, 2, 3,
4, or 5, y=2x+1), and each R can be different (e.g.,
Ti(N(CH.sub.3)(C.sub.2H.sub.5)).sub.4). A precursor for a metal
oxide other than titanium oxide can also be selected from any
suitable compounds. In general, an alkylamino precursor such as
tetrakis-dimethylaminotitanium (TDMAT) can provide a higher film
growth rate than does an alkoxy precursor such as titanium
tetraisopropoxide (TTIP) because a precursor having a smaller
molecular size such as TDMAT tends to have less sterific hindrance
so as to have more adsorption sites as compared with a precursor
having a greater molecular size such as TTIP. Since ALD is a
self-limiting adsorption reaction process, the amount of deposited
precursor molecules is determined by the number of reactive surface
sites and is independent of the precursor exposure after
saturation, and a supply of the precursor is such that the reactive
surface sites are saturated thereby by each pulse. The deposition
temperature may be in a range of about 0 to about 200.degree. C.,
which temperature is compatible with photoresist (e.g., does not
cause thermal damage to photoresist). A reactant gas may be
selected from the group consisting of O.sub.2, NH.sub.3, N.sub.2O,
and/or H.sub.2. More than one reactant gas can be used for forming
a metal oxide hardmask. A reactant gas flow rate may be in a range
of about 100 to about 5,000 sccm. A carrier gas for the precursor
may be in a range of about 200 to about 5,000 sccm. A deposition
pressure may be in a range of about 100 to about 1,000 Pa. RF power
may be in a range of about 50 to about 500 W for direct plasma, or
more than 1 kW for remote plasma. A precursor bottle (or tank)
temperature and delivery line may be controlled at a temperature of
about 0 to about 200.degree. C. In some embodiments, reaction
energy can be supplied not only by means of plasma ignition, but
also by means of UV irradiation.
[0057] Additionally, certain treatment can be performed before or
during the deposition process, wherein treatment gas may be
selected from the group consisting of O.sub.2, NH.sub.3, H.sub.2,
N.sub.2, N.sub.2O, He, and/or Ar.
[0058] The reactor temperature can be set differently (e.g., higher
than that set for deposition) for reactor cleaning in order to
increase cleaning speed.
[0059] In some embodiments, SDDP can be performed as follows:
[0060] FIGS. 4A to 4G schematically illustrate SDDP processes.
First, pre-patterned features 41 (e.g., photoresist) are formed on
a base film (hardmask or BARC) 42 as shown in FIG. 4A. Next, an
integrated spacer film 43 (which is also referred to generally as
"hardmask") which is a conformal film is deposited according to any
of the disclosed embodiments to cover the pre-patterned features 41
and the base film 42 as shown in FIG. 4B. The integrated film
spacer has a desired ratio of thickness at the top to thickness at
the bottom. A spacer will be a film layer formed on a sidewall of
the pre-patterned feature 41. In order to form a spacer,
anisotropic spacer etching is conducted as shown in FIG. 4C to
remove all the film material on the bottom surface and the top
surface including the slanted surfaces, i.e., all the horizontal
surfaces and slanted surfaces at the top, leaving only the material
on the sidewalls (43a). Because the thickness of the film at the
slanted surfaces and the thickness of the film at the bottom
surface are such that portions of the film at the slanted surface
and at the bottom surface are removed by etching nearly at the same
time, after removing the original pre-patterned features 41,
complete removal of the residual portion at the top is realized,
and only the spacer is left on the base film 42 as shown in FIG.
4D. The inner wall 43b of the spacer does not have an overhang
portion at the top edge. Using the spacer 43a, anisotropic etching
is performed for pattern transfer as shown in FIG. 4E, wherein a
pattern transfer layer 44 is formed on a substrate 45. Because
according to some embodiments, the spacer has sufficient etch
selectivity relative to the base film, and no overhang portion is
formed, the distance between the top edges of the spacer and the
distance between the vertical portions of the spacer are
substantially or nearly the same (.+-.20% or less, .+-.10% or less,
or .+-.5% or less), and the pattern transfer layer (target film) 44
is accurately etched in the vertical direction. According to some
embodiments of the preset invention, the spacer 43b is less likely
to collapse than a conventional spacer during a drying process
after rinsing. That is, complete removal of the residual portion is
achieved, and critical dimension (CD) variation can be minimized
and a precise width 46 can be obtained as shown in FIG. 4F.
Further, according to some embodiments, the spacer can easily be
removed by etching as shown in FIG. 4G. Further, when the metal
contained in the spacer is subjected to fluoridation when the
reactor is cleaned with a fluorine-containing gas, the metal
fluoride is not solid at a reactor-cleaning temperature, and thus,
it can easily be removed from an inner wall of the reactor.
[0061] FIG. 6 is a schematic representation of an apparatus usable
in some embodiments. In this example, by providing a pair of
electrically conductive flat-plate electrodes 64, 62 in parallel
and facing each other in the interior 71 of a reaction chamber 63,
applying RF power 65 to one side, and electrically grounding 72 the
other side, a plasma is excited between the electrodes. A
temperature regulator is provided in a lower stage (which also
serves as the lower electrode 62), and a temperature of a substrate
61 placed thereon is kept constant at a given temperature. The
upper electrode 64 serves as a shower plate as well, and the
reactant gas (C) and additive/purge gas (B), if any, are introduced
into the reaction chamber 63 through gas flow controllers 181, 182,
respectively, and the shower plate. Also the precursor (A) is
introduced into the reaction chamber 63 through a gas flow
controller 183, a pulse flow control valve 31, and the shower
plate. Additionally, in the reaction chamber 63, an exhaust pipe 66
is provided through which gas in the interior 71 of the reaction
chamber 63 is exhausted. Additionally, the reaction chamber is
provided with a seal gas flow controller (now shown) to introduce
seal gas into the interior 71 of the reaction chamber 63. A
separation plate for separating a reaction zone and a transfer zone
in the interior of the reaction chamber is omitted from this
schematic figure. The seal gas is not required but is used in some
embodiments for aiding in preventing reaction gas from
communicating with the lower part of the chamber below the
separation plate.
[0062] For the pulse flow control valve 31, a pulse supply valve
can effectively be used for PE-ALD. This apparatus can also be used
for PE-CVD. The pulse control valve can be provided for the
reactant gas (C) and/or the additive/purge gas (B). Further, RF
power can be pulsed. In the above, the pulsing of the RF power can
be accomplished by adjusting a matching box (not shown). The RF
power requires a minimum time period for discharging, which is
typically as short as 8 msec. Thus, by adjusting the matching box,
the duration of the RF power can easily be controlled at about 0.1
sec, for example.
[0063] In some embodiments, the average thickness deposited per
cycle may be about 0.6 nm/cycle to about 1.0 nm/cycle. The pulse
supply of the precursor can be continued until a desired thickness
of film is obtained. If the desired thickness of film is about 20
nm to about 100 nm, about 20 cycles to about 150 cycles (e.g.,
about 40 to about 100 cycles) may be conducted.
[0064] A remote plasma unit can be connected to the apparatus,
through which an etching gas or a process gas can be supplied to
the interior of the apparatus through the showerhead 64.
[0065] As described above in relation to FIG. 1D, the causes of
pattern collapsing are expected to be: 1) the template height is
too high to maintain a spacer during subsequent dry etching, 2) the
mechanical properties of a spacer film are poor, e.g., its elastic
modulus and hardness are so low as to cause deformation easily, and
3) the difference in film stress between the spacer film and the
core material is so great as to result in pattern collapsing. In
some embodiments, the above causes of pattern collapsing can be
eliminated by using a spacer comprising, represented by, made
predominately of, consisting essentially of, constituted by, or
equivalent to any of the metal oxides explicitly, necessarily, or
inherently disclosed herein. For example, as shown in FIG. 8B,
since a metal oxide such as TiO.sub.2 as a hardmask has high etch
selectivity against an underlying template/hardmask 82, the height
of the hardmask constituted by TiO.sub.2 can be significantly low
as compared to that of a hardmask constituted by SiO (FIG. 8A). In
FIG. 8A, since the etch selectivity of the SiO spacer 83 as a
template (the SiO.sub.2 spacer is not considered to be a hardmask
due to its low dry etch resistivity) is not high, the height of the
template needs to be great, resulting in a tall vertical spacer in
step (a) which corresponds to step (d) in FIG. 4D (steps (b) to (d)
in FIGS. 4B to 4D are referred to as "spacer defined double
patterning"). When etching the template/hardmask 82 using the
spacer 83 in step (b) to transfer a patter to the template/hardmask
82, the vertical spacer 83 tends to be at least partially collapsed
or deformed. If the vertical spacer is deformed or collapsed, the
pattern transfer is not performed accurately, resulting in
inaccurate etching of a target layer 81 in step (c). In FIG. 8B,
since the metal oxide spacer has high etch selectivity, an etched
template for forming the spacer thereon (see, e.g., a
template/hardmask 91 in step (b) of FIG. 9) can be short and thus
can be sustained during etching to form a vertical spacer 84 (metal
oxide spacer) in step (a). Thus, steps (b) and (c) can be performed
accurately. In some embodiments, preferably, the height of the
vertical spacer (i.e., the thickness of a template to be patterned
by etching) may be in a range of about 50 nm to about 400 nm,
typically about 80 nm to about 200 nm, and the thickness of the
vertical spacer may be in a range of about 3 nm to about 60 nm,
typically about 5 nm to about 40 nm. Further, the metal oxide
spacer has high elastic modulus and hardness (as measured as a
film) (preferably an elastic modulus of about 70 GPa to about 400
GPa, typically about 100 GPa to about 200 GPa, and a hardness of
about 5 GPa to about 20 GPa, typically about 6 GPa to about 15
GPa), and thus, the spacer can be sustained during dry etching.
[0066] Additionally, the film stress of the metal oxide (as
measured as a film) can be controlled by changing the duration of
RF application and/or RF power, and the film stress can be changed
from tensile to compressive and can minimize pattern deformation,
so that the difference in film stress between the spacer film
(which constitutes vertical spacers) and the core material (which
is a photoresist material of a template remaining in spaces
surrounded by the vertical spacers in step (d) in FIG. 9) can be
minimized, thereby inhibiting pattern collapsing. In some
embodiments, the film stress of the spacer film as measured as a
planar film and the film stress of the core material as measured as
a planar film may be substantially or nearly the same, or
equivalent, or less than about 100 MPa, or less than about 50 MPa.
The film stresses are equivalent if the differences therebetween
are so small as to inhibit pattern collapsing in SDDP, for example.
In some embodiments, the film stress of the template is first
determined, and then, a desired film stress of the spacer is
determined, and accordingly, deposition conditions for the spacer
are determined to adjust the film stress of the spacer to the
desired value as a function of RF power and/or the duration of RF
power.
[0067] In this disclosure, the term "template" refers to a film to
be processed such as a film subjected to patterning or formation of
holes, and the term "hardmask" refers to a film having high etch
resistivity, e.g., about five times higher than a template to be
etched, so that the film can effectively protect a certain portion
of the template from being etched. The "hardmask" may be referred
to as an "etch mask".
[0068] In some embodiments, the use of nitrogen-containing gas such
as NH.sub.3 and N.sub.2 as a reactant gas increases a film growth
rate in PEALD for a metal oxide such as TiO.sub.2. Further, the use
of nitrogen-containing gas can significantly increase wet etch rate
(preferably 2 to 20 times, typically 4 to 8 times, higher than the
standard thermal oxide), but can effectively maintain dry etch
resistance (as dry etch rate, preferably about 1/100 to about 1/5,
typically about 1/50 to about 1/10, of that of the standard thermal
oxide), which are highly beneficial to subsequent spacer removal.
In some embodiments, nitrogen-containing gas is used in a flow rate
of about 100 sccm to about 2,000 sccm, typically about 200 sccm to
about 1,000 sccm, typically in combination with oxygen gas
(preferably about 200 sccm to about 1,000 sccm). In some
embodiments, the flow rate of nitrogen-containing gas is less than
50% of total reactant gas but more than 10% (typically 20% to
35%).
[0069] As discussed above, according to some embodiments, at least
one of the following benefits can be realized: By adding
low-frequency RF (LRF) (such as about 200 MHz to about 1,000 MHz,
typically about 300 MHz to about 600 MHz) at a power ratio of LRF
to total RF of about 1 to about 30, film stress can be more
effectively controlled. By controlling plasma ignition conditions
(e.g., power and/or ignition time per cycle), film stress and wet
etch rate can effectively be controlled. By using
nitrogen-containing reactant gas, film properties can effectively
be tuned or adjusted.
[0070] FIG. 9 is a schematic representation of pattern transfer and
target etching using space defined double patterning (SDDP)
according to another embodiment of the present invention, wherein
the metal oxide film is used as a hardmask between templates to
transfer a pattern from the first template to the second template.
A template/hardmask 91 is used for increasing pattern density
(e.g., pitch reduction) in SDDP processes. A template/hardmask 82
is used as a hardmask for etching a target layer 81. A hardmask 92
is used for transferring a pattern from the template/hardmask 91 to
the template/hardmask 82. In step (a) in FIG. 9, on a bottom
antireflective coating (BARC) 94, a photoresist pattern 93 is
formed so that the template/hardmask 91 can be etched in the
photoresist pattern in step (b) which is a step of transferring a
pattern to the template/hardmask 91. In step (c), a metal oxide
spacer 95 is deposited according to any of the disclosed
embodiments or equivalents thereto, followed by etching in step (d)
which is a spacer RIE step. By stripping the material of the
template/hardmask 91 (a photoresist material in the core portions
96), vertical spacers are formed in step (e). Steps (e) to (g) in
FIG. 9 correspond to steps (a) to (c) in FIG. 8B (although the
height of the vertical spacer is exaggerated). That is, in step
(f), the pattern is transferred to the template/hardmask 82, and in
step (g), the target layer 81 is subjected to dry etch. In the
above, by using a metal oxide according to any of the disclosed
embodiments or equivalents thereto as the hardmask 92, the pattern
can effectively be transferred from the template/hardmask 91 to the
template/hardmask 82. In some embodiments, a planar hardmask such
as the hardmask 92 may be deposited by any of the methods disclosed
herein or equivalents thereof or by pulsed PECVD.
[0071] The embodiments will be explained with reference to specific
examples which are not intended to limit the present invention. The
numerical numbers applied in the specific examples may be modified
by a range of at least .+-.50% in other conditions, wherein the
endpoints of the ranges may be included or excluded.
EXAMPLE
Example 1
[0072] A metal oxide hardmask film was formed on a substrate
(.PHI.200 mm) by PE-ALD under the conditions shown below using the
PE-ALD apparatus illustrated in FIG. 6. The sequence in each cycle
of PE-ALD is shown in FIG. 7.
TABLE-US-00001 TABLE 1 Precursor Titanium tetra-isopropoxide
Deposition temperature 50 deg C. Reactant gas flow O.sub.2, 500
sccm Carrier gas flow Ar, 2000 sccm Deposition pressure 200 Pa RF
power (27.12 MHz) 50 W Deposition process sequence Step 1: Step 2:
Step 3: Step 4: Precursor feed Precursor purge RF ignition Post
purge 0.9 sec 2.0 sec 0.5 sec 0.5 sec
[0073] A SiO hardmask (LT-SiO) was also formed on a substrate by
PE-ALD under conditions substantially the same as above.
[0074] Dry etch selectivity and wet etch selectivity of each
hardmask (also those of standard thermal oxide) were measured, and
the results are shown below.
TABLE-US-00002 TABLE 2 Thermal oxide PEALD LT-SiO PEALD TiO.sub.2
Dry etch rate 0.20 1.00 0.11 (NF.sub.3, 100 deg C.) Wet etch rate
0.09 1.00 0.10 (DHF 1:100)
[0075] Hardness and Elastic modulus of each hardmask were also
measured, and the results are shown below.
TABLE-US-00003 TABLE 3 PEALD LT-SiO PEALD TiO.sub.2 EM (GPa) 41.6
158.7 Hardness (GPa) 3.6 9.8
[0076] As shown in the above tables, the TiO hardmask has
substantially high dry/wet etch selectivity relative to that of the
LT-SiO hardmask. The wet etch selectivity of the TiO hardmask was
substantially comparable to that of the standard thermal oxide, and
the dry etch rate of the TiO hardmask was substantially lower than
that of the LT-SiO hardmask. Further, the mechanical strength of
the TiO hardmask was substantially higher than that of the LT-SiO
hardmask, indicating that the spacer-collapsing problem can
effectively be avoided.
Example 2
[0077] In the same manner as described in Example 1 except for the
conditions shown in Table 4 below, films were deposited to compare
film growth rates using titanium tetraisopropoxide (TTIP) and
tetrakis-dimethylaminotitanium (TDMAT). As can be seen from the
table, the film growth rate by TDMAT was nearly two times higher
(2-3, 2-4) than that by TTIP (2-1, 2-2). The properties of the
obtained film by TDMAT were comparable with those by TTIP, although
the wet etch rate of the film by TDMAT was increased by about two
to three times that by TTIP. Additionally, by prolonging the RF
ignition time (2-5), the mechanical strength was increased and the
wet etch rate was reduced.
TABLE-US-00004 TABLE 4 2-1 2-2 2-3 2-4 2-5 Precursor TTIP TTIP
TDMAT TDMAT TDMAT RF power 50 W 100 W 50 W 100 W 100 W RF ignition
time per cycle 0.4 sec 0.4 sec 0.4 sec 0.4 sec 2.0 sec GPC
(nm/cycle) 0.042 0.042 0.079 0.074 0.059 RI 2.401 2.407 2.281 2.308
2.415 WER Ratio 0.75 0.84 2.79 1.47 0.64 (1:100 DHF) compared to
thermal oxide Hardness (GPa) 9.01 9.39 8.10 8.90 12.70 EM (GPa)
160.6 167.5 130.2 147.0 190.1 Film stress (MPa, 388.8 370.6 226.6
227.8 181.8 Tensile = +) GPC: Growth rate per cycle; RI: Refractive
index; WER: Wet etch rate; DHF: Dilute hydrofluoric acid; EM:
Elastic modulus
Example 3
[0078] In the same manner as described in Example 1 except for the
conditions shown in Tables 5 and 6 below, films were deposited to
confirm controllability of film stress. As can be seen from Table
6, the film stress was well controlled by changing plasma-on time
(duration of RF ignition) and/or plasma power (RF power),
indicating that the films obtained using TTIP are suitable as a
spacer having pattern-collapsing resistance. That is, by increasing
the plasma-on time, the degree of tensile stress of the film can be
reduced, and by increasing plasma power, the degree of tensile
stress of the film can be reduced and can even be changed to
compressive stress.
TABLE-US-00005 TABLE 5 TiO.sub.2 Source TTIP 23 sccm Reactant gas
Oxygen 500 sccm Carrier gas Ar 2000 sccm Pressure 200 Pa RF power
Variable (X) W Source feed Purge 1 Plasma on Purge 2 0.3 sec 0.6
sec Variable (Y) sec 0.1 sec
TABLE-US-00006 TABLE 6 Process Precursor Plasma power Plasma-on
temperature supply (X) time (Y) Film stress 100 deg C. TTIP 50 W
0.4 sec +388 MPa 100 deg C. TTIP 50 W 2.0 sec +161 MPa 100 deg C.
TTIP 100 W 0.4 sec +275 MPa 100 deg C. TTIP 300 W 0.4 sec -268
MPa
Example 4
[0079] In the same manner as described in Example 1 except for the
conditions shown in Table 7 below, films were deposited to evaluate
effects of NH.sub.3 on properties of the films.
[0080] As can be seen from Table 5 below, when adding NH.sub.3 to
oxygen as a reactant (4-3, 4-4), the film growth rate was increased
(by over 20%), and the dry etch rate of the film was significantly
decreased (by over 70%), whereas the wet etch rate of the film was
surprisingly increased (by over 600%) as compared with that without
NH.sub.3 (4-1, 4-2), indicating that the film is suitable as a
spacer which has chemical resistance but is easily removable.
Additionally, the properties of the films obtained using less
NH.sub.3 (4-3) and more NH.sub.3 (4-4) than oxygen appear to be
similar.
TABLE-US-00007 TABLE 7 Precursor: TTIP 4-1 4-2 4-3 4-4 Process
condition O.sub.2 500 sccm O.sub.2 1000 sccm O.sub.2 500 sccm
O.sub.2 500 sccm NH.sub.3 0 sccm NH.sub.3 0 sccm NH.sub.3 250 sccm
NH.sub.3 1000 sccm GPC (nm/cycle) 0.042 0.042 0.055 0.052 RI 2.401
2.407 2.179 2.177 WER Ratio 0.75 0.84 6.38 5.45 (1:100 DHF)
compared to thermal oxide DER Ratio 0.24 0.27 0.07 0.06
(100.degree. C. NF.sub.3) compared to thermal oxide Hardness (GPa)
9.01 9.39 6.79 6.82 EM (GPa) 160.6 167.5 114.5 113.7 Film stress
(MPa, 388.8 370.6 312.4 303.3 Tensile = +)
Example 5
[0081] In addition to Example 1, SiN hardmasks were formed by
PE-ALD at 400.degree. C. and at 100.degree. C., respectively, and a
TEOS hardmask was also formed by PE-ALD at 380.degree. C.,
according to conventional recipes, and the mechanical strength of
the resultant hardmasks was measured. The results are shown in FIG.
5. As can be seen from FIG. 5, the TiO hardmask has a substantially
higher elastic modulus than that of the SiN hardmask at 100.degree.
C. and the TEOS hardmask, and the hardness of the TiO hardmask is
comparable to that of the SiN hardmask at 100.degree. C. and the
TEOS hardmask. Since the TiO hardmask has a significantly high
elastic modulus, the spacer collapse problem can effectively be
avoided (elastic modulus is more important than hardness in terms
of prevention of spacer collapse). Additionally, the TiO hardmask
has significant advantages as compared with the SiN hardmask at
100.degree. C. and the TEOS hardmask in terms of deposition rate,
conformality, etch selectivity, etc. For example, the SiN hardmask
at 100.degree. C. has a good etch selectivity relative to a base
film, but it is not easy to remove by etching. The TEOS hardmask
does not have a good etch selectivity relative to a base film. The
SiN hardmask at 400.degree. C. has higher mechanical strength than
the TiO hardmask. However, the deposition temperature of
400.degree. C. causes thermal damage to a template or photoresist,
and further, copper or other metal diffusion or migration is likely
to be a problem. Further, removing the SiN hardmask at 400.degree.
C. is not easy, and even at 400.degree. C., the deposition rate is
low. In view of the above, the TiO hardmask is significantly
superior to the other hardmasks.
Example 6
[0082] In the same manner as in Example 5 except for the conditions
shown in Table 8 below, films were deposited to evaluate elastic
modulus and hardness of the films. As can be seen from the table, a
film of TiO.sub.2 shows excellent elastic modulus even though the
deposition temperature was low, and also the film shows as good
hardness as a SiN film and significantly better hardness than a SiO
film.
TABLE-US-00008 TABLE 8 Material Elastic Modulus Hardness TiO.sub.2
PEALD 100 deg C. 175 GPa 10.3 GPa SiO PECVD 380 deg C. 80 GPa 10.3
GPa PEALD 75 deg C. 45.3 GPa 4.3 GPa ALD 450 deg C. 56.4 GPa 5.1
GPa SiN PEALD 100 deg C. 108 GPa 11.7 GPa PEALD 400 deg C. 243 GPa
31 GPa
Example 7
[0083] In the same manner as in Example 1 except for the conditions
shown in Table 9 below, films were deposited to evaluate refractive
index (at 633 nm) and average growth rate (nm/cycle) of the films,
wherein an ALD cycle ratio of the number of cycles for TiO.sub.2 to
the total number of cycles for TiO.sub.2 and SiO.sub.2 per unit
cycle for one layer of multi-element film was changed from 0/1 to
1/1 (i.e., 0/1, 1/3, 1/2, 2/3, and 1/1). In the above, a ratio of
1/3 refers to a unit cycle constituted by two SiO.sub.2 cycles,
followed by one TiO.sub.2 cycle; a ratio of 1/1 refers to a unit
cycle constituted by one SiO.sub.2 cycle, followed by one TiO.sub.2
cycle; and a ratio of 2/3 refers to a unit cycle constituted by one
SiO.sub.2 cycle, followed by two TiO.sub.2 cycles, wherein each
unit cycle was repeated at desired times.
TABLE-US-00009 TABLE 9 SiO.sub.2 cycle Source BDEAS 26 sccm
Reactant gas Oxygen 500 sccm Carrier gas Ar 2000 sccm Pressure 200
Pa RF power 100 W Source feed Purge 1 Plasma on Purge 2 0.3 sec 0.6
sec 0.4 sec 0.1 sec TiO.sub.2 cycle Source TTIP 23 sccm Reactant
gas Oxygen 500 sccm Carrier gas Ar 2000 sccm Pressure 200 Pa RF
power 100 W Source feed Purge 1 Plasma on Purge 2 0.3 sec 0.6 sec
0.4 sec 0.1 sec
[0084] As shown in FIG. 10, it was confirmed that by changing the
ALD cycle ratio (e.g., in any ranges defined by any two values of
the above ratios or any two numbers of 0.1 to 0.9 in 0.1
increments), the refractive index and the growth rate of the
resultant films could be adjusted at desired levels, although the
relationship between the refractive index and the ALD cycle ratio
and the relationship between the growth rate and the ALD cycle
ratio were reversed.
[0085] The present invention can include, but is not limited to,
the following additional embodiments and advantages:
[0086] In order to avoid spacer collapse, mechanically robust
materials other than those disclosed above can be used.
[0087] In order to avoid spacer collapse, footing reduction can be
performed. FIGS. 3A and 3B is a schematic representation
illustrating in-situ footing reduction where (a) reactive ion etch
(RIE) (FIG. 3A) and (b) ashing (FIG. 3B) are conducted. In step
(a), a spacer film is deposited by PE-ALD on a photoresist and a
base film, and in-situ interface control is conducted, thereby
performing in-situ footing reduction of the spacer film, wherein a
top surface of a photoresist 33 and a part of a base film 31 are
exposed, and a spacer 32 does not have extended footing. In step
(b), by ashing, the photoresist 33 is removed, thereby forming the
spacer 32' having reduced footing, decreasing CD changes. The metal
oxide hardmask selected in some embodiments of the present
invention is effective for footing reduction.
[0088] In order to avoid spacer collapse, adhesion between the
spacer and the base film can be enhanced. Enhancing adhesion can be
accomplished by forming an adhesion layer or treating a surface of
the base film. The metal oxide hardmask selected in some
embodiments of the present invention is effective for enhancing
adhesion.
[0089] All processes can be done sequentially in one PE-ALD
reactor, including pre-bake, trimming, adhesion control, deposition
and surface control, thereby achieving high productivity and low
cost.
[0090] Dry etch rate and mechanical strength can be controlled by
combining multiple materials.
[0091] In-situ reactor self cleaning can be performed by selecting
a metal whose fluoride has high vapor pressure at room temperature
(unlike AlF.sub.3), thereby achieving high productivity and low
cost. The metal oxide hardmask selected in some embodiments of the
present invention is effective for easy self cleaning.
[0092] The deposition process is ALD so that 100% conformality,
less pattern loading, and good uniformity can effectively be
achieved.
[0093] Since ALD dielectric materials have been widely studied, it
is possible to select good candidate materials without undue burden
by using at least one or all of the criteria disclosed in the
embodiments.
[0094] Generally, thermal ALD is very challenging at low
temperatures such as less than 400.degree. C. because chemical
reactivity decreases with temperature. PE-ALD is advantageous at
low temperatures, and a conformal film can be formed. Unlike
thermal ALD, PE-ALD can deposit different materials on a substrate
at the same temperature. Also for this reason, PE-ALD is
advantageous. Thermal reaction cannot effectively control film
composition and precursor adsorption. PE-ALD can control each film
quality by tuning process conditions. Good process controllability
and good process reliability can be realized by using PE-ALD.
Incidentally, a catalyst used as an aid of deposition is usually
not useful in either thermal or PE-ALD, and thus, no catalyst is
used.
[0095] A preferred metal oxide is expressed by
Si.sub.xTi.sub.(1-x)O.sub.y wherein O.ltoreq.x<1, y.about.2. A
WO or TaO hardmask can be used. Additionally, a TiN, WN, or TaN
hardmask may be used in combination with those disclosed
herein.
[0096] It will be understood by those of skill in the art that
numerous and various modifications can be made without departing
from the spirit of the present invention. Therefore, it should be
clearly understood that the forms of the present invention are
illustrative only and are not intended to limit the scope of the
present invention.
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